Nasa's Goddard Space Centre have released an animation of what they believe Mars to have been like four billion years ago. Much like Earth at the time, Nasa believe Mars was a land of rolling clouds and lakes, but no life. The video shows the gradual transformation of the red planet to a barren rock as it slowly lost its atmosphere.

This week on 90 second science we look at the announcement that 2013 is one of the hottest years on record, continuing a trend of remarkable warming since 1998. We also take a look at an animation released by Nasa showing what they believe Mars used to look like four billion years ago, and a new scanner which police can use to identify hidden weapons in public places and at long range.